Welcome to Android Central! Yes, you can stream MP4 videos, but flv is trickier, since it's Flash, which is not officially supported in Android. There are some workarounds, but they don't always work for all devices.
Downloading files from filesharing sites is supported (although exercise caution, since those are good places to catch malware).
You can transfer files from device to device via Bluetooth.
Connecting an external USB hard drive requires the device to be compatible with OTG cables, so ask about that before you buy.
12-14-2014 01:13 AM